The present disclosure relates generally to the field of wind turbine or windmill devices for the conversion of a flow power from a stream of air or other fluid into rotary mechanical power and, more specifically, to wind turbine devices of the horizontal axis type having a plurality of helical blades. In a preferred aspect of this disclosure, wind turbine blade assemblies and devices are provided wherein the helical blades are offset from the axis of rotation of the blade assembly. In an especially preferred embodiment, the radial distance between the axis of rotation and the radially inward edge of the helical blades is approximately equal to one-half the radial thickness of the blades.